Project Summary Preterm birth (PTB) is the leading cause of perinatal morbidity and mortality in developed countries [13]. Research in human pregnancy has demonstrated that maternal stress during pregnancy is associated with increased risk for PTB, with increasing evidence of the specific biological mediating processes [5]. During pregnancy, the placenta synthesizes corticotropin releasing hormone (pCRH) and secretes it into the maternal bloodstream at accelerating rates [3]. Placental CRH increases in maternal blood until reaching a threshold that contributes to the triggering of labor and delivery [4]. Evidence suggests that premature rises in pCRH levels pose risk for PTB [5]. Maternal stress during pregnancy may contribute to PTB risk through premature increases in pCRH [5]. Several studies have pointed to pregnancy anxiety as a significant and strong independent risk factor for shorter gestational length [1, 9, 23]. Pregnancy anxiety is defined as anxiety specific to the current pregnancy [8]. Anxiety symptoms in general frequently co-occur with depressive symptoms [10]. However, less is known about depressive symptoms during pregnancy and pCRH production. To date, no studies have examined the combined contributions of pregnancy anxiety and depressive symptoms to pCRH levels or trajectories over pregnancy, and their joint role in risk for earlier birth. The objective of the proposed study is to investigate the effect of pregnancy anxiety and depressive symptoms on gestational length (GL), and use repeated measurements of pCRH across pregnancy to examine both trajectories and levels of pCRH as potential mediators of links between prenatal depressive symptoms and pregnancy anxiety, and GL. The study will also explore the role of race/ethnicity and SES, an important area of research that has implications for understanding the role of risk factors and etiology of PTB in populations traditionally underrepresented in research. The proposed study will utilize interview data and blood samples collected from 229 women over pregnancy in the Healthy Babies Before Birth (HB3) study, a longitudinal study that follows mothers at three times in pregnancy and three times over the first year postpartum recruited in the Los Angeles and Denver metropolitan areas. In person interview assessments of depressive and anxiety symptoms, and pregnancy anxiety with standardized scale are conducted during the pregnancy. Maternal blood samples are collected at each trimester of pregnancy, and plasma samples have been banked for future pCRH assays. Data collection is projected to be completed in June 2018. As such, by July 2018, serum samples can be assayed. Examining how anxiety and depression are disruptive to the normative physiological processes of pregnancy, and increase risk for PTB, has implications for understanding PTB etiology and targeting interventions to serve pregnant women at risk.